It is known to drive and steer tracked vehicles by transmitting power from a power-driven shaft to track sprocket output shafts via respective planetary gear sets, a steering shaft holding one of the sun gear, planet gear-carrier, and ring gear elements of each planetary gear set against rotation for straight travel of the vehicle and rotating said one element of the planetary gear sets in opposite directions for turning the vehicle.
The following U.S. patents exemplify driving and steering systems of this type:
U.S. Pat. Nos. 1,395,004, Oct. 25, 1921, Norelius; 2,196,368, Apr. 9, 1940, Thomson; 3,450,218, June 17, 1969, Looker; 3,530,741, Sept. 29, 1970, Charest; 4,471,669, Sept. 18, 1984, Seaberg.
It is also known to drive and steer army tanks and bulldozers using a power differential and a steering differential which are geared together to increase and decrease the speeds of the sprocket axles when the steering shaft is rotated by an auxiliary motor and worm drive. This system is shown and described in an article entitled "Tanks and dozers turn on a dime with new all-gear steering" on pages 60 to 62 of the July, 1985 issue of "Popular Science".